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Charge separation relative to the reaction plane in Pb-Pb collisions at ffiffiffiffiffiffiffiffiffis NN p ¼2:76TeVB.Abelev et al.*(ALICE Collaboration)(Received 5July 2012;published 2January 2013)Measurements of charge-dependent azimuthal correlations with the ALICE detector at the LHC arereported for Pb-Pb collisions at ffiffiffiffiffiffiffiffis NN p ¼2:76TeV .Two-and three-particle charge-dependent azimuthal correlations in the pseudorapidity range j j <0:8are presented as a function of the collision centrality,particle separation in pseudorapidity,and transverse momentum.A clear signal compatible with a charge-dependent separation relative to the reaction plane is observed,which shows little or no collision energy dependence when compared to measurements at RHIC energies.This provides a new insight for under-standing the nature of the charge-dependent azimuthal correlations observed at RHIC and LHC energies.DOI:10.1103/PhysRevLett.110.012301PACS numbers:25.75.Ld,11.30.Er,11.30.Qc,12.38.AwThe possibility to observe parity violation in the strong interaction using relativistic heavy-ion collisions has been discussed for many years [1–3].In quantum chromody-namics (QCD),this symmetry violation originates in the interaction between quarks and topologically nontrivial gluonic fields,instantons,and sphalerons [4].This interac-tion,which is characterized by the topological charge [5],breaks the balance between the number of quarks with different chirality,resulting in a violation of the P and CP symmetry.In [6,7],it was suggested that in the vicinity of the deconfinement phase transition,and under the influ-ence of the strong magnetic field generated by the colliding nuclei,the quark spin alignment along the direction of the angular momentum (i.e.the direction of the magnetic field)and the imbalance of the left-and right-handed quarks,generates an electromagnetic current.The experimental search of these effects has intensified recently,following the realization that the consequent quark fragmentation into charged hadrons results in a charge separation along the direction of the magnetic field,and perpendicular to the reaction plane (the plane of symmetry of a collision defined by the impact parameter vector and the beam direction).This phenomenon is called the chiral magnetic effect (CME).Because of fluctuations in the sign of the topologi-cal charge,the resulting charge separation averaged over many collisions is zero.This makes the observation of the CME possible only via P -even observables,expressed in terms of two-particle and multiparticle correlations.The previous measurement of charge separation by the STAR Collaboration [8]is consistent with the qualitative expec-tations for the CME and has triggered an intense discussion [9–13].A significant source of uncertainty in the theoretical consideration of the CME is related to the expected center-of-mass energy dependence.In [7],the authors argued that the uncertainty in making any quantitative prediction relies on the time integration over which the magnetic field develops and decays.As long as a decon-fined state of matter is formed in a heavy-ion collision,the magnitude of the effect should either not change or should decrease with increasing energy [7].In addition,in [12]it is also suggested that there should be no energy depen-dence between the top RHIC and the LHC energies,based on arguments related to the universality of the underlying physical process,without however explicitly quantifying what the contribution of the different values and time evolution of the magnetic field for different energies will be.On the other hand,in [13]it is argued that the CME should strongly decrease at higher energies,because the magnetic field decays more rapidly.Such spread in the theoretical expectations makes it important to measure the charge-dependent azimuthal correlations at the LHC,where the collision energy is an order of magnitude higher compared to the RHIC.In this Letter we report the measurement of charge-dependent azimuthal correlations at midrapidity in Pb-Pb collisions at the center-of-mass energy per nucleon pair ffiffiffiffiffiffiffiffis NN p ¼2:76TeV by the ALICE Collaboration at the LHC.Azimuthal correlations among particles produced in a heavy-ion collision provide a powerful tool for the experi-mental study of particle production with respect to the reaction plane.They are usually quantified by the aniso-tropic flow coefficients,v n ,in a Fourier decomposition [14].Local violation of parity symmetry may result in the additional P -odd sinus terms [3,8,15]:dNd’ $1þ2X n ½v n; cos ðn Á’ Þþa n; sin ðn Á’ Þ ;(1)where Á’ ¼’ ÀÉRP is the azimuthal angle ’ of the charged particle of type relative to the reaction plane*Full author list given at the end of the article.Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0License .Further distri-bution of this work must maintain attribution to the author(s)and the published article’s title,journal citation,and DOI.angle,ÉRP.The leading order coefficient a1; reflects the magnitude while the higher orders(a n; for n>1)describe the specific shape in azimuth of the effects from local parity violation.We thus employ a multiparticle correlator [15]that probes the magnitude of the a1coefficient,and at the same time suppresses the background correlations unrelated to the reaction plane:h cosð’ þ’ À2ÉRPÞi¼h cosÁ’ cosÁ’ iÀh sinÁ’ sinÁ’ i:(2) The indices and refer to the charge of the particles.The brackets denote an average over the particle pairs within the event as well as an average over the analyzed events.In practice,the reaction plane angle is not known and is esti-mated by constructing the event plane using azimuthal par-ticle distributions.In Eq.(2),the terms h cosÁ’ cosÁ’ i and h sinÁ’ sinÁ’ i quantify the correlations in-and out-of plane,respectively.The latter is sensitive to the charge correlations resulting from the CME:h sinÁ’ sinÁ’ i$ h a1; a1; i.The construction of the correlator in Eq.(2)as the difference between these two contributions suppresses correlations not related to the reaction plane orientation (nonflow).The contribution from the CME to the correla-tions of pairs of particles with same and opposite charge is expected to be similar in magnitude and opposite in sign. This expectation could be further modified by the medium created in a heavy-ion collision,that may result in the dilution of the correlations between particles with opposite sign[6,7].In order to evaluate each of the two terms in Eq.(2),we also measure the two-particle correlator:h cosð’ À’ Þi¼h cosÁ’ cosÁ’ iþh sinÁ’ sinÁ’ i;(3) which in contrast to the correlator in Eq.(2)is independent of the reaction plane angle and susceptible to the large P-even background contributions.The combination of these correlators provides access to both components, h cosÁ’ cosÁ’ i and h sinÁ’ cosÁ’ i,which is impor-tant for detailed comparisons with model calculations.It should be pointed out that both correlators of Eq.(2) and Eq.(3)could be affected by background sources.In [10],it is argued that the effect of momentum conservation influences in a similar way the pairs of particles with opposite and same charge,and could result in a potentially significant correction to both h cosð’ þ’ À2ÉRPÞi and h cosð’ À’ Þi.Also in[10],it was suggested that local charge conservation effects may be responsible for a sig-nificant part of the observed charge dependence of the correlator h cosð’ þ’ À2ÉRPÞi.Recent calculations [16]suggest that the correlator in Eq.(2)may have a negative(i.e.out-of-plane),charge-independent,dipole flow contribution originating fromfluctuations in the initial energy density of a heavy-ion collision.A description of the ALICE detector and its perform-ance can be found in[17,18].For this analysis,the follow-ing detector subsystems were used:the time projection chamber(TPC)[19],the silicon pixel detector(SPD), two forward scintillator arrays(VZERO),and two zero degree calorimeters(ZDC)[17].We analyzed a sample of about13Â106minimum-bias trigger events of Pb-Pb collisions atffiffiffiffiffiffiffiffis NNp¼2:76TeV collected with the ALICE detector.The standard ALICE offline event selection criteria[20]were applied,including a collision vertex cut ofÆ7cm along the beam axis.The collision centrality is estimated from the amplitude mea-sured by the VZERO detectors[17].The data sample is divided into centrality classes which span0%-70%of the hadronic interaction cross section,with the0%-5%class corresponding to the most central(i.e.smaller impact pa-rameter)collisions.Charged particles reconstructed by the TPC are accepted for analysis within j j<0:8and0:2< p T<5:0GeV=c.A set of requirements described in[20] were applied in order to ensure the quality of the tracks but also to reduce the contamination from secondary particles. To evaluate the systematic uncertainties in the analysis, events recorded with two different magneticfield polarities were analyzed leading to an uncertainty that is less than7% for all centrality classes.The cut on the collision vertex was varied fromÆ7cm toÆ10cm from the nominal collision point,with steps of1cm,contributing a maximum of5%to the total uncertainty.A bias due to the centrality determina-tion was studied by using multiplicities measured by the TPC or the SPD,rather than the VZERO,and was found to be less than10%.Contamination due to secondary tracks that do not originate from the collision vertex was reduced by requiring that the distance of closest approach between tracks and the primary vertex is less than2cm.The effect of secondary tracks on the measurement was estimated by varying the cut from2to4cm in steps of0.5cm and was calculated to be below15%.Effects due to nonuniform acceptance of the TPC were estimated to be below2%and are corrected for in the analysis.A significant contribution to the systematic error is coming from the uncertainty in the v2measurement,which is used as an estimate of the reaction plane resolution.The v2 estimate is obtained from the2-and4-particle cumulant analyses[20],which are affected in different ways by non-flow effects andflowfluctuations.For this analysis,v2was taken as the average of the two values,with half of the difference between v2f2g and v2f4g being attributed as the systematic uncertainty.The values of this uncertainty range from9%for the20%–30%centrality to18%(24%)for the 50%–60%(60%–70%)centrality class.The differences in the results from the four independent analysis methods (described below)were also considered as part of the system-atic uncertainty and were estimated to be3%for the 20%–30%and the50%–60%centrality bins and47%for the most peripheral centrality class.The contributions from all effects were added in quadrature to calculate the totalsystematic uncertainty.For the correlation between pairs of particles with the same charge it varies from 19%(28%)for the 20%–30%(50%–60%)centrality up to 55%for the 60%–70%centrality class.The correlations between oppo-site charged particles for 0%–60%centrality and for the same charge pairs for 0%–20%centrality are compatible with zero with a systematic error below 5:5Â10À5.Figure 1(a)presents the centrality dependence of the three-particle correlator,defined in Eq.(2).The correla-tions of the same charge pairs for the positive-positive and negative-negative combinations are found to be consistent within statistical uncertainties and are combined into one set of points,labeled same .The difference between the correlations of pairs with same and opposite charge indi-cates a charge dependence with respect to the reaction plane,as may be expected for the CME.To test the bias from the reaction plane reconstruction,four independent analyses were performed.The first analysis uses a cumu-lant technique [21],whereas for the three other analyses the orientation of the collision symmetry plane is estimated from the azimuthal distribution of charged particles in the TPC,and hits in the forward VZERO and ZDC detectors [22].There is a very good agreement between the results obtained with the event plane estimated from different detectors covering a wide range in pseudorapidity.This allows us to conclude that background sources due to corre-lations not related to the orientation of the reaction plane are negligible,with perhaps the exception of the peripheral collisions for the pairs of particles with opposite charge.Figure 1(b)shows the centrality dependence of the two-particle correlator h cos ð’ À’ Þi ,as defined in Eq.(3),which helps to constrain experimentally the P -even back-ground correlations.The statistical uncertainty is smaller than the symbol size.The two-particle correlations for the same and opposite charge combinations are always posi-tive and exhibit qualitatively similar centrality depen-dence,while the magnitude of the correlation is smaller for the same charged pairs.Our two-particle correlation results differ from those reported by the STARCollaboration for Au-Au collisions at ffiffiffiffiffiffiffiffis NN p ¼200GeV [8]for which negative correlations are observed for the same charged pairs.Figure 1(c)shows the h cosÁ’ cosÁ’ i and h sinÁ’ sinÁ’ i terms separately.For pairs of particles of the same charge,we observe that the h sinÁ’ sinÁ’ i correlations are larger than the h cosÁ’ cosÁ’ i ones.On the other hand,for pairs of opposite charge,the two terms are very close except for the most peripheral collisions.Further interpretation of the results presented in Fig.1(c)in terms of in-and out-of-plane correlations is complicated due to the significant nonflow contribution in h cos ð’ À’ Þi .Figure 2presents the three-particle correlator h cos ð’ þ’ À2ÉRP Þi as a function of the collision centrality com-pared to model calculations and results for RHIC energies.The statistical uncertainties are represented by the errorbars.The shaded area around the points indicates the systematic uncertainty based on the different sources described above.Also shown in Fig.2are STAR results [8].The small difference between the LHC and the RHIC data indicates little or no energy dependence for the three-particle correlator when changing from the collisionenergy of ffiffiffiffiffiffiffiffis NN p ¼0:2TeV to 2.76TeV .In Fig.2,the ALICE data are compared to the expectations from the HIJING model [23].The HIJING results for the three-particle correlations are divided by the experimentally〉)R P Ψ - 2βϕ + αϕ c o s (〈-0.50.5-3〉)βϕ-αϕ c o s (〈00.0020.0040.006centrality, %0.0020.003FIG.1(color online).(a)Centrality dependence of the correla-tor defined in Eq.(2)measured with the cumulant method and from correlations with the reaction plane estimated using the TPC,the ZDC,and the VZERO detectors.Only statistical errors are shown.The points are displaced slightly in the horizontal direction for visibility.(b)Centrality dependence of the two-particle corre-lator defined in Eq.(3)compared to the STAR data [8].The width of the solid red lines indicates the systematic uncertainty of the ALICE measurement.(c)Decomposition of the correlators into h cosÁ’ cosÁ’ i and h sinÁ’ sinÁ’ i terms.The ALICE results in (b)and (c)are obtained with the cumulant method.measured value of v 2(i.e.h cos ð’ þ’ À2’c Þi =v 2f 2g )as reported in [20]due to the absence of collective azimuthal anisotropy in this model.Since the points do not exhibit any significant difference between the correlations of pairs with same and opposite charge,they were averaged in the figure.The correlations from HIJING show a significant increase in the magnitude for very peripheral collisions.This can be attributed to correlations not related to the reaction plane orientation,in particular,from jets [8].The results from ALICE in Fig.2show a strong corre-lation for pairs with the same charge and simultaneously a very weak correlation for the pairs of opposite charge.This difference in the correlation magnitude depending on the charge combination could be interpreted as ‘‘quenching’’of the charge correlations for the case when one of the particles is emitted toward the center of the dense medium created in a heavy-ion collision [6,7].An alternative ex-planation can be provided by a recent suggestion [16]that the value of the charge-independent version of the corre-lator defined in Eq.(2)is dominated by directed flow fluctuations.The sign and the magnitude of these fluctua-tions based on a hydrodynamical model calculation for RHIC energies [16]appear to be very close to the mea-surement.Our results for charge-independent correlations are given by the shaded band in Fig.2.The thick solid line in Fig.2shows a prediction [13]for the same sign correlations due to the CME at LHC ener-gies.The model makes no prediction for the absolute magnitude of the effect and can only describe the energy dependence by taking into account the duration and time evolution of the magnetic field.It predicts a decrease of correlations by about a factor of 5from RHIC to LHC,which would significantly underestimate the observed magnitude of the same sign correlations seen at the LHC.At the same time in [7,12],it was suggested that the CME might have the same magnitude at the LHC and at RHIC energies.Figure 3shows the dependence of the three-particle correlator on the transverse momentum difference,j p T ; Àp T ; j ,the average transverse momentum,ðp T ; þp T ; Þ=2,and the pseudorapidity separation,j À j ,of the pair for the 30%-40%centrality range.The pairs of opposite charge do not show any significant dependence on the pseudorapidity difference,while there is a dependencecentrality, %〉)R P Ψ - 2βϕ + αϕ c o s (〈-0.6-0.4-0.200.20.40.6-3FIG.2(color online).The centrality dependence of the three-particle correlator defined in Eq.(2).The circles indicate the ALICE results obtained from the cumulant analysis.The stars show the STAR data from [8].The triangles represent the three-particle correlations [h cos ð’ þ’ À2’c Þi ]from HIJING [23]corrected for the experimentally measured v 2f 2g [20].Points are displaced horizontally for visibility.A model prediction for the same sign correlations incorporating the chiral magnetic effect for LHC energies [13]is shown by the solid line.The shaded band represents the centrality dependence of the charge-independent correlations.)| (GeV/c T,β - p T,α|p 〉)R P Ψ - 2βϕ + αϕc o s (〈-0.4-0.20.2-3))/2 (GeV/c T,β + p T,α(p |βη - αη = |η∆FIG.3(color online).The three-particle correlator defined in Eq.(2)as a function of (a)the transverse momentum difference,j p T ; Àp T ; j ,(b)the average transverse momentum,ðp T ; þp T ; Þ=2,and (c)the rapidity separation,j À j ,of the charged particle pair of same (closed symbols)and opposite (open symbols)sign.on j p T ; Àp T ; j (stronger)and ðp T ; þp T ; Þ=2(weaker).The correlations for pairs of particles of the same charge show no strong dependence on the p T difference,allowing one to exclude any type of short range correlations (e.g.quantum statistics correlations)as the main source of the effect.In addition,it is seen that the magnitude of the same charge correlations increases with increasing average p T of the pair.This observation is in contradiction to the initial expectations from theory [7]that the effect should originate from low p T particles.The dependence of the correlations on the j À j indicates a width of one unit in pseudor-apidity,beyond which the value of h cos ð’ þ’ À2ÉRP Þi is close to zero up to Á %1:5.Similar results were reported also at RHIC energies [8].At the moment there are no quantitative model calculations of the charge-dependent differential correlations.In summary,we have measured the charge-dependentazimuthal correlations in Pb-Pb collisions at ffiffiffiffiffiffiffiffis NN p ¼2:76TeV at the LHC using the ALICE detector.Both two-and three-particle correlations are reported.A clear signal compatible with a charge-dependent separation rela-tive to the reaction plane is observed.However,our results are not described by the only available quantitative model prediction of the CME for the LHC energy.The lack of realistic model calculations for the centrality and pair differential dependencies based on models incorporating CME and possible background contributions does not allow us to make a firm conclusion regarding the nature of the charge-dependent correlations originally observed at RHIC and now established at the LHC.The observation of a small collision energy dependence of the three-particle correlation and the simultaneous significant change in the two-particle correlations between top RHIC and LHC energies put stringent constraints on models built to interpret such correlations.Analyses of higher harmonic correlations are planned and may yield a better understanding of the com-plex charge-dependent correlations 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Roman,74G.Cara Romeo,17W.Carena,6F.Carena,6N.Carlin Filho,75F.Carminati,6A.Casanova Dı´az,54J.Castillo Castellanos,40J.F.Castillo Hernandez,26E.A.R.Casula,76V.Catanescu,25 C.Cavicchioli,6C.Ceballos Sanchez,77J.Cepila,2P.Cerello,16B.Chang,37,78S.Chapeland,6J.L.Charvet,40S.Chattopadhyay,10S.Chattopadhyay,64I.Chawla,5M.Cherney,79C.Cheshkov,6,80B.Cheynis,80V.Chibante Barroso,6D.D.Chinellato,81P.Chochula,6M.Chojnacki,57S.Choudhury,10P.Christakoglou,56 C.H.Christensen,47P.Christiansen,82T.Chujo,53S.U.Chung,83C.Cicalo,84L.Cifarelli,8,6,18F.Cindolo,17J.Cleymans,70F.Coccetti,18F.Colamaria,22D.Colella,22G.Conesa Balbastre,34Z.Conesa del Valle,6 P.Constantin,27G.Contin,73J.G.Contreras,74T.M.Cormier,63Y.Corrales Morales,50P.Cortese,85I.Corte´s Maldonado,86M.R.Cosentino,66F.Costa,6M.E.Cotallo,58E.Crescio,74P.Crochet,39E.Cruz Alaniz,9E.Cuautle,87L.Cunqueiro,54A.Dainese,55,31H.H.Dalsgaard,47A.Danu,88D.Das,64K.Das,64I.Das,65S.Dash,89A.Dash,81S.De,10G.O.V.de Barros,75A.De Caro,90,18G.de Cataldo,91J.de Cuveland,21A.De Falco,76D.De Gruttola,90H.Delagrange,32A.Deloff,92V.Demanov,69N.De Marco,16E.De´nes,7 S.De Pasquale,90A.Deppman,75G.D.Erasmo,22R.de Rooij,57M.A.Diaz Corchero,58D.Di Bari,22T.Dietel,28C.Di Giglio,22S.Di Liberto,93A.Di Mauro,6P.Di Nezza,54R.Divia`,6Ø.Djuvsland,23A.Dobrin,63,82T.Dobrowolski,92I.Domı´nguez,87B.Do¨nigus,26O.Dordic,94O.Driga,32A.K.Dubey,10A.Dubla,57L.Ducroux,80P.Dupieux,39M.R.Dutta Majumdar,10A.K.Dutta Majumdar,64D.Elia,91D.Emschermann,28。
电坏处英语作文The Disadvantages of Electronics。
In today's modern world, electronics have become an integral part of our daily lives. From smartphones to laptops to televisions, we are constantly surrounded by electronic devices. While these devices have undoubtedly made our lives more convenient, they also come with their fair share of disadvantages.One of the biggest drawbacks of electronics is their negative impact on our health. The blue light emitted by screens can disrupt our sleep patterns and cause eye strain. Prolonged use of electronic devices has also been linked to an increased risk of obesity, as it often leads to a sedentary lifestyle. Additionally, the constant exposure to electromagnetic radiation from electronic devices hasraised concerns about its potential long-term effects onour health.Another disadvantage of electronics is their contribution to environmental pollution. Electronic devices contain hazardous materials such as lead, mercury, and cadmium, which can leach into the soil and water when improperly disposed of. The manufacturing process of electronics also generates a significant amount of electronic waste, further adding to the environmental burden.Furthermore, the widespread use of electronics has led to a decline in face-to-face communication. Many people now prefer to communicate through text messages and social media, rather than having meaningful conversations in person. This has resulted in a lack of interpersonal skills and has made it difficult for people to form genuine connections with others.In addition, the constant need to upgrade to the latest electronic devices has led to a culture of consumerism and materialism. People are often pressured to keep up with the latest trends, leading to unnecessary spending and a disregard for the environmental impact of constantlydiscarding old devices.Moreover, the overreliance on electronic devices has made us more vulnerable to cyber threats. Hacking, identity theft, and online scams have become increasingly common, putting our personal and financial information at risk.In conclusion, while electronics have undoubtedly revolutionized the way we live, it is important to recognize and address their disadvantages. From their impact on our health and the environment to their influence on our social interactions and consumer behavior, it is crucial to find a balance between the benefits and drawbacks of electronic devices. By being mindful of these disadvantages, we can work towards using electronics in a more responsible and sustainable manner.。
Title: The Legacy of James Clerk MaxwellJames Clerk Maxwell, a brilliant scientist of the 19th century, revolutionized our understanding of electromagnetism and paved the way for future technological advancements. Born in Scotland, Maxwell's curiosity and dedication to scientific inquiry led him to groundbreaking discoveries that are still relevant today.Maxwell's most significant contribution was his theory of electromagnetism, which unified the previously separate fields of electricity and magnetism. His mathematical equations, known as Maxwell's equations, described the behavior of electromagnetic fields with precision and elegance. These equations are the foundation of modern electronics, telecommunications, and even relativity theory.Moreover, Maxwell's prediction of electromagnetic waves was a pivotal moment in the history of science. His calculations suggested that these waves, traveling through space at the speed of light, could exist. This prediction not only explained the phenomenon of light but also foretold the existence of radio waves, which later became the basis of wireless communication.Beyond his scientific achievements, Maxwell's legacy lies in his approach to research. He was a meticulous experimentalist, always striving to verify his theoretical predictions through rigorous experiments. His dedication to the scientific method and his commitment to precision set an example for future generations of scientists.In conclusion, James Clerk Maxwell's contributions to science are immeasurable. His theory of electromagnetism and prediction of electromagnetic waves have transformed our world, laying the foundation for modern technology. His legacy remains alive in the scientific community, inspiring us to continue exploring the wonders of the natural world.。
a rXiv:n ucl-t h /441v28Ma y2The decay ρ0→π++π−+γand the coupling constant g ρσγA.Gokalp ∗and O.Yilmaz †Physics Department,Middle East Technical University,06531Ankara,Turkey(February 8,2008)Abstract The experimental branching ratio for the radiative decay ρ0→π++π−+γis used to estimate the coupling constant g ρσγfor a set of values of σ-meson parameters M σand Γσ.Our results are quite different than the values of this constant used in the literature.PACS numbers:12.20.Ds,13.40.HqTypeset using REVT E XThe radiative decay processρ0→π++π−+γhas been studied employing different approaches[1,5].There are two mechanisms that can contribute to this radiative decay: thefirst one is the internal bremsstrahlung where one of the charged pions from the decay ρ0→π++π−emits a photon,and the second one is the structural radiation which is caused by the internal transformation of theρ-meson quark structure.Since the bremsstrahlung is well described by quantum electrodynamics,different methods have been used to estimate the contribution of the structural radiation.Singer[1]calculated the amplitude for this decay by considering only the bremsstrahlung mechanism since the decayρ0→π++π−is the main decay mode ofρ0-meson.He also used the universality of the coupling of theρ-meson to pions and nucleons to determine the coupling constant gρππfrom the knowledge of the coupling constant gρter,Renard [3]studied this decay among other vector meson decays into2π+γfinal states in a gauge invariant way with current algebra,hard-pion and Ward-identities techniques.He,moreover, established the correspondence between these current algebra results and the structure of the amplitude calculated in the single particle approximation for the intermediate states.In corresponding Feynman diagrams the structural radiation proceeds through the intermediate states asρ0→S+γwhere the meson S subsequently decays into aπ+π−pair.He concluded that the leading term is the pion bremsstrahlung and that the largest contribution to the structural radiation amplitude results from the scalarσ-meson intermediate state.He used the rough estimate gρσγ≃1for the coupling constant gρσγwhich was obtained with the spin independence assumption in the quark model.The coupling constant gρππwas determined using the then available experimental decay rate ofρ-meson and also current algebra results as3.2≤gρππ≤4.9.On the other hand,the coupling constant gσππwas deduced from the assumed decay rateΓ≃100MeV for theσ-meson as gσππ=3.4with Mσ=400MeV. Furthermore,he observed that theσ-contribution modifies the shape of the photon spectrum for high momenta differently depending on the mass of theσ-meson.We like to note, however,that the nature of theσ-meson as a¯q q state in the naive quark model and therefore the estimation of the coupling constant gρσγin the quark model have been a subject ofcontroversy.Indeed,Jaffe[6,7]lately argued within the framework of lattice QCD calculation of pseudoscalar meson scattering amplitudes that the light scalar mesons are¯q2q2states rather than¯q q states.Recently,on the other hand,the coupling constant gρσγhas become an important input for the studies ofρ0-meson photoproduction on nucleons.The presently available data[8] on the photoproduction ofρ0-meson on proton targets near threshold can be described at low momentum transfers by a simple one-meson exchange model[9].Friman and Soyeur [9]showed that in this picture theρ0-meson photoproduction cross section on protons is given mainly byσ-exchange.They calculated theγσρ-vertex assuming Vector Dominance of the electromagnetic current,and their result when derived using an effective Lagrangian for theγσρ-vertex gives the value gρσγ≃2.71for this coupling ter,Titov et al.[10]in their study of the structure of theφ-meson photoproduction amplitude based on one-meson exchange and Pomeron-exchange mechanisms used the coupling constant gφσγwhich they calculated from the above value of gρσγinvoking unitary symmetry arguments as gφσγ≃0.047.They concluded that the data at low energies near threshold can accommodate either the second Pomeron or the scalar mesons exchange,and the differences between these competing mechanisms have profound effects on the cross sections and the polarization observables.It,therefore,appears of much interest to study the coupling constant gρσγthat plays an important role in scalar meson exchange mechanism from a different perspective other than Vector Meson Dominance as well.For this purpose we calculate the branching ratio for the radiative decayρ0→π++π−+γ,and using the experimental value0.0099±0.0016for this branching ratio[11],we estimate the coupling constant gρσγ.Our calculation is based on the Feynman diagrams shown in Fig.1.Thefirst two terms in thisfigure are not gauge invariant and they are supplemented by the direct term shown in Fig.1(c)to establish gauge invariance.Guided by Renard’s[3]current algebra results,we assume that the structural radiation amplitude is dominated byσ-meson intermediate state which is depicted in Fig. 1(d).We describe theρσγ-vertex by the effective LagrangianL int.ρσγ=e4πMρMρ)2 3/2.(3)The experimental value of the widthΓ=151MeV[11]then yields the value g2ρππ2gσππMσ π· πσ.(4) The decay width of theσ-meson that follows from this effective Lagrangian is given asΓσ≡Γ(σ→ππ)=g2σππ8 1−(2Mπ2iΓσ,whereΓσisgiven by Eq.(5).Since the experimental candidate forσ-meson f0(400-1200)has a width (600-1000)MeV[11],we obtain a set of values for the coupling constant gρσγby considering the ranges Mσ=400-1200MeV,Γσ=600-1000MeV for the parameters of theσ-meson.In terms of the invariant amplitude M(Eγ,E1),the differential decay probability for an unpolarizedρ0-meson at rest is given bydΓ(2π)31Γ= Eγ,max.Eγ,min.dEγ E1,max.E1,min.dE1dΓ[−2E2γMρ+3EγM2ρ−M3ρ2(2EγMρ−M2ρ)±Eγfunction ofβin Fig.5.This ratio is defined byΓβRβ=,Γtot.= Eγ,max.50dEγdΓdEγ≃constant.(10)ΓσM3σFurthermore,the values of the coupling constant gρσγresulting from our estimation are in general quite different than the values of this constant usually adopted for the one-meson exchange mechanism calculations existing in the literature.For example,Titov et al.[10] uses the value gρσγ=2.71which they obtain from Friman and Soyeur’s[9]analysis ofρ-meson photoproduction using Vector Meson Dominance.It is interesting to note that in their study of pion dynamics in Quantum Hadrodynamics II,which is a renormalizable model constructed using local gauge invariance based on SU(2)group,that has the sameLagrangian densities for the vertices we use,Serot and Walecka[14]come to the conclusion that in order to be consistent with the experimental result that s-waveπN-scattering length is anomalously small,in their tree-level calculation they have to choose gσππ=12.Since they use Mσ=520MeV this impliesΓσ≃1700MeV.If we use these values in our analysis,we then obtain gρσγ=11.91.Soyeur[12],on the other hand,uses quite arbitrarly the values Mσ=500 MeV,Γσ=250MeV,which in our calculation results in the coupling constant gρσγ=6.08.We like to note,however,that these values forσ-meson parameters are not consistent with the experimental data onσ-meson[11].Our analysis and estimation of the coupling constant gρσγusing the experimental value of the branching ratio of the radiative decayρ0→π++π−+γgive quite different values for this coupling constant than used in the literature.Furthermore,since we obtain this coupling constant as a function ofσ-meson parameters,it will be of interest to study the dependence of the observables of the reactions,such as for example the photoproduction of vector mesons on nucleonsγ+N→N+V where V is the neutral vector meson, analyzed using one-meson exchange mechanism on these parameters.AcknowledgmentsWe thank Prof.Dr.M.P.Rekalo for suggesting this problem to us and for his guidance during the course of our work.We also wish to thank Prof.Dr.T.M.Aliev for helpful discussions.REFERENCES[1]P.Singer,Phys.Rev.130(1963)2441;161(1967)1694.[2]V.N.Baier and V.A.Khoze,Sov.Phys.JETP21(1965)1145.[3]S.M.Renard,Nuovo Cim.62A(1969)475.[4]K.Huber and H.Neufeld,Phys.Lett.B357(1995)221.[5]E.Marko,S.Hirenzaki,E.Oset and H.Toki,Phys.Lett.B470(1999)20.[6]R.L.Jaffe,hep-ph/0001123.[7]M.Alford and R.L.Jaffe,hep-lat/0001023.[8]Aachen-Berlin-Bonn-Hamburg-Heidelberg-Munchen Collaboration,Phys.Rev.175(1968)1669.[9]B.Friman and M.Soyeur,Nucl.Phys.A600(1996)477.[10]A.I.Titov,T.-S.H.Lee,H.Toki and O.Streltrova,Phys.Rev.C60(1999)035205.[11]Review of Particle Physics,Eur.Phys.J.C3(1998)1.[12]M.Soyeur,nucl-th/0003047.[13]S.I.Dolinsky,et al,Phys.Rep.202(1991)99.[14]B.D.Serot and J.D.Walecka,in Advances in Nuclear Physics,edited by J.W.Negeleand E.Vogt,Vol.16(1986).TABLESTABLE I.The calculated coupling constant gρσγfor differentσ-meson parametersΓσ(MeV)gρσγ500 6.97-6.00±1.58 8008.45±1.77600 6.16-6.68±1.85 80010.49±2.07800 5.18-9.11±2.64 90015.29±2.84900 4.85-10.65±3.14 90017.78±3.23Figure Captions:Figure1:Diagrams for the decayρ0→π++π−+γFigure2:The photon spectra for the decay width ofρ0→π++π−+γ.The contributions of different terms are indicated.Figure3:The pion energy spectra for the decay width ofρ0→π++π−+γ.The contri-butions of different terms are indicated.Figure4:The decay width ofρ0→π++π−+γas a function of minimum detected photon energy.Figure5:The ratio Rβ=Γβ。
LOGO第一章记叙文体的英译与写作第二章法律文体的英译与写作第三章应用文体英译与写作第四章广告文体英译与写作QQ:105448245424学时科技英语(二)EST ⅡREFERENCES:1、张梦井，杜耀文汉英科技翻译指南，航空工业出版社，19962、王运，实用科技英语翻译技巧，科技文献出版社，19923、熊第霖，英文科技写作，国防工业出版社，20011 记叙文体的汉译英1. 1 科技论文的汉译英问题1. 2 摘要的英译与写作1. 3 国际会议文献的英译与写作1. 1 科技论文的汉译英问题一、科技论文的分类◆按学科的性质和功能⏹基础学科论文⏹技术学科论文⏹应用学科论文◆按照写作目的和发挥的作用⏹学术性论文⏹技术性论文⏹学位论文◆按论文内容所属学科数学论文物理论文化学论文天文学论文机械工程技术论文建筑工程技术论文◆按研究和写作方法理论推导型实(试)验研究型观测型设计计算型发现发明型争鸣型综述型Title标题Abstract摘要Keywords关键词Table of contents目录Nomenclature术语表Introduction引言正文Acknowledgement致谢Reference参考文献Appendix附录Methods方法Results结果Discussion讨论Conclusion结论二、科技论文的一般结构LOGOacknowledgmentReferencesTitle 标题Author 作者Abstract 摘要Introduction 引言4 Summary and conclusion三、论文标题的英译与写作1、标题的作用⏹Generalizing the Text⏹Attracting the Reader⏹Facilitating the Retrieval2、标题的长度（单词总数）及词性⏹标题不宜过长，大多为12个单词以内。
⏹标题中用得最多的是名词（包括动名词），除名词外，用得较多的是介词，有时使用形容词、冠词、连词、副词。
Versions of this article appeared in Power Quality Magazine, Sep 1999 and PCIM Magazine Feb 2000 CURRENT-LIMITING FUSES IMPROVE POWER QUALITYbyR. WilkinsOverdee, Rocky Lane Heswall, Wirral, CH60 0BZ, UKH.C.ClineGould Shawmut, 374 Merrimac Street Newburyport, MA01950INTRODUCTIONVoltage sags (sometimes called voltage dips) in power networks due to power system short-circuit faults can cause serious problems for computer systems, adjustable-speed drives, and other industrial and domestic systems [1,2]. The cost of downtime and incorrect operation of equipment is becoming increasingly important. A recent study showed that major industrial users in South Africa suffer annual losses of more than $200 million due to voltage sags [3].The effect of a voltage sag is dependent upon its magnitude and duration. A curve published by the Information Technology Industry Council (ITIC, formerly known as CBEMA), is often used as a yardstick for the assessment of voltage sags. This curve, shown in Fig.1, defines overvoltage and undervoltage limits as a function of time. The region in between these two limits is a region of acceptable power quality. Although the ITIC (CBEMA) curve is strictly applicable only to 120V single-phase equipment subject to very specific types of voltage waves, it is nevertheless a useful general guide for other power systems.For a bolted fault to ground the faulted bus voltage will drop to zero. Fig.1 shows that for this case the duration of the fault must be less than 20ms to fall within the ITIC (CBEMA) limits. It follows that the operating speed of protection systems plays a key role in mitigating the effects of voltage sags and the improving of power quality [2,3,4]. The high-speed clearance provided by current-limiting fuses, which have no moving parts, can make a significant contribution to the improvement of power quality.OPERATION OF CURRENT-LIMITING FUSESCurrent-limiting fuses have been used for many years to provide high-speed protection of low-voltage and medium-voltage power systems. Fig.2 illustrates the construction of a typical modern current-limiting fuse. The fuse elements are typically made from silver or copper strip, and have reduced cross-sectional areas in a number of places. They are surrounded by compacted quartz sand in an insulating tube. When a short-circuit fault occurs, the reduced cross-sectional areas heat up and melt very quickly and form a number of electric arcs, which are then controlled and eventually quenched and extinguished by the surrounding sand. The appearance of the arcs corresponds electrically to the sudden switching of the fuse from a low-resistance state to a high-resistance state. This causes a rapid reduction in circuit current, limiting the peak current whichis permitted to flow in the circuit, and consequently limiting the “let-through I2t”. This is the integral of the square of the current over the fault period, and is a measure of the energy which must be absorbed by the circuit components. Fig.3 is a typical test oscillogram showing the breaking of a short-circuit fault current in an a.c. circuit. During the pre-arcing period the current closely follows the available current wave, the voltage drop across the fuse being low. However when arcing begins the fuse resistance and voltage increase rapidly, and the current is forced down to zero well before the natural zero of the prospective current wave.The peak system current is limited to a level well below the peak available current, dramatically reducing the heating and electromagnetic forces experienced by the power system components. REDUCTION OF VOLTAGE SAG DURATIONThe reduction of heating and electromagnetic stresses (both of which depend upon the square of the current) in power systems protected by current-limiting fuses is well known.However, it is not generally realized that current-limiting fuses make an important contribution to the improvement of power quality, because they also reduce the duration of voltage sags caused by short-circuit faults.As an example, consider the simple system shown in Fig.4. This represents a typical motor control center with 2 smaller motors (M1 and M2) and 2 larger motors (M3 and M4), protected by current-limiting fuses rated at 150% of the motor full-load current. For a fault at bus 6, (on the terminals of M4), bus 2 is the "point of common coupling", as far as the other parallel-connected motor loads are concerned [1].Fig.5 shows the effects on the voltage at bus 2 of a 3-phase short-circuit fault at bus 6, with M1 and M3 initially lightly loaded and M2 and M4 fully loaded. The fault is cleared by operation of the 3 fuses in line 5. These results were computed using the method described in [5], which uses a standard fuse model and takes into account 3-phase effects in the operation of the fuses as well as motor electrical and mechanical transients.When the fault occurs the voltage at the common bus 2 sags to a low level, but only for a few milliseconds, until the fuses melt. In the cases shown the melting times are 9.2,5.2 and 3.3ms, so the sag duration is well within the ITIC (CBEMA) limit shown in Fig.1. After the fuses switch to the arcing mode the bus voltage is raised due to the appearance of the fuse arc voltages, and the fault currents in the three phases are forced to zero. The highest peak current in line 5 is 13.7 p.u. It is necessary that the voltages produced by fuse operation are not so high as to be in the upper region of unacceptable power quality. The waveshape of the voltage transients produced during fuse operation is non-standard as far as the ITIC (CBEMA) curve is concerned, but if we approximate them as half-sine waves of medium frequency they correspond to r.m.s. values of 1.45, 1.53 and 1.34 per-unit with durations of 2.5, 3.4 and 1.34 milliseconds. These points are close to the upper ITIC (CBEMA) curve, but do not suggest any significant problem [1].The raising of the bus voltage during the fuse arcing phase aids the re-acceleration of the parallel-connected motors. During the fault the speed of the unfaulted motors does not drop significantly.If the fault had been at the terminals of one of the smaller motors, M1 or M2, clearance of the fault by the corresponding (smaller) fuses would be faster still, with even less disturbance to the system. The system data used here is typical of such systems. However, for very weak systems, with a very large supply impedance, the short-circuit current may be too low to cause fuse operation in less than one half-cycle [1].NON-CURRENT-LIMITING PROTECTIVE DEVICESDevices such as circuit-breakers or expulsion fuses have a different operating principle. The switching arc is extinguished at a current zero of the a.c. wave. This may take several a.c. cycles and during this period no significant current limitation occurs.Fig.6 shows the computed interruption transients for the example system if the current-limiting fuses are replaced by non-current-limiting devices which produce negligible arc voltage and which take about 2½ cycles to clear the fault. The high peak after the first quarter-cycle is composed of the fault current from the source via line 1 plus contributions from all the parallel-connected motors. There is no current limitation, which gives higher thermal and electromagnetic stresses on the circuit components. The peak network current is 21 p.u. while the I2t let through after the fault is cleared is almost 10 times higher than if the circuit were protected by the fuse.In this case the voltage at bus 2 sags to about 0.15-0.22 per-unit for 41-46 milliseconds, which is well in the lower region of unacceptable power quality shown in Fig.1. However bus 2 voltage remains depressed even after the fault has been cleared. It increases slowly from about 0.6 per-unit and remains below the ITIC (CBEMA) curve for a considerable time. The reason for this is that the speed of the parallel-connected motors drops significantly during the long-duration voltage sag. After the fault is removed the motors re-accelerate, drawing a high current from the supply, which causes the duration of the voltage sag at bus 2 to be further extended. This effect has also been noted in measurements on a utility network [4].Fig.7 shows how these results relate to the ITIC curve. For each data point an approximate r.m.s. value of voltage has been plotted for the corresponding time duration.CONCLUSIONCurrent-limiting fuses provide protection against disruptive heating and electromagnetic effects, but also make an important contribution to the improvement of power quality. They achieve this by operating within one half-cycle, to limit the duration of voltage sags, and without producing unacceptably high voltages. The resulting short duration of the disturbance to the system avoids further depression of voltages due to motor re-acceleration.Using fuses to improve the power quality of a power system is also a very inexpensive option.For systems where the cost of installing uninterruptible power supplies and similar types ofequipment cannot be justified, high-speed protection by current-limiting fuses is veryeconomical way of mitigating the effects of voltage sags.REFERENCES[1]M.H.J. Bollen. "Voltage sags : effects, mitigation and prediction" Power Engineering Journal , June 1996, pp 129-135. [2] R. Wilkins and M.H.J. Bollen. "The role of current-limiting fuses in power qualityimprovement" 3rd International Conference on Power Quality , Amsterdam, 24-27October 1994.[3] G. Topham. "Influence of the design and operation of protection and control on powerquality". Power Engineering Journal , December 1998, pp 253-258.[4] Lj.A Kojovic, S.P. Hassler, K.L. Leix, C.W. Williams and E.E. Baker. "Comparativeanalysis of expulsion and current-limiting fuse operation in distribution systems forimproved power quality and protection" IEEE Transactions on Power Delivery 1997.Paper PE-770-PWRD-0-06-1007.[5]R. Wilkins, A.J. McDonald and M. Castillo. "Computation of short-circuit transients inindustrial networks protected by current-limiting fuses". 8th International Symposium onShort-Circuit Currents in Power Systems , Brussels, 8-10 October 1998. 00.511.522.533.544.550.00010.0010.010.1110100duration , secp.u.voltage Fig.1 ITIC (CBEMA) curve.Fig.2 Construction of a typical current-limiting fuse.Fig. 4. Example system.Fig.5 Transients in system protected by current-limiting fuses.Fig.6 Transients in system protected by non-current-limiting devices. 0.5233.544.50.0001 0.001 0.01 0.1 1 10 100 duration , sec p.u. voltageFig.7 Voltage sags and peaks in relation to ITIC curve.Below is given annual work summary, do not need friends can download after editor deleted Welcome to visit againXXXX annual work summaryDear every leader, colleagues:Look back end of XXXX, XXXX years of work, have the joy of success in your work, have a collaboration with colleagues, working hard, also have disappointed when encountered difficulties and setbacks. Imperceptible in tense and orderly to be over a year, a year, under the loving care and guidance of the leadership of the company, under the support and help of colleagues, through their own efforts, various aspects have made certain progress, better to complete the job. For better work, sum up experience and lessons, will now work a brief summary.To continuously strengthen learning, improve their comprehensive quality. With good comprehensive quality is the precondition of completes the labor of duty and conditions. A year always put learning in the important position, trying to improve their comprehensive quality. Continuous learning professional skills, learn from surrounding colleagues with rich work experience, equip themselves with knowledge, the expanded aspect of knowledge, efforts to improve their comprehensive quality.The second Do best, strictly perform their responsibilities. Set up the company, to maximize the customer to the satisfaction of the company's products, do a good job in technical services and product promotion to the company. And collected on the properties of the products of the company, in order to make improvement in time, make the products better meet the using demand of the scene.Three to learn to be good at communication, coordinating assistance. On‐site technical service personnel should not only have strong professional technology, should also have good communication ability, a lot of a product due to improper operation to appear problem, but often not customers reflect the quality of no, so this time we need to find out the crux, and customer communication, standardized operation, to avoid customer's mistrust of the products and even the damage of the company's image. Some experiences in the past work, mentality is very important in the work, work to have passion, keep the smile of sunshine, can close the distance between people, easy to communicate with the customer. Do better in the daily work to communicate with customers and achieve customer satisfaction, excellent technical service every time, on behalf of the customer on our products much a understanding and trust.Fourth, we need to continue to learn professional knowledge, do practical grasp skilled operation. Over the past year, through continuous learning and fumble, studied the gas generation, collection and methods, gradually familiar with and master the company introduced the working principle, operation method of gas machine. With the help of the department leaders and colleagues, familiar with and master the launch of the division principle, debugging method of the control system, and to wuhan Chen Guchong garbage power plant of gas machine control system transformation, learn to debug, accumulated some experience. All in all, over the past year, did some work, have also made some achievements, but the results can only represent the past, there are some problems to work, can't meet the higher requirements. In the future work, I must develop the oneself advantage, lack of correct, foster strengths and circumvent weaknesses, for greater achievements. Looking forward to XXXX years of work, I'll be more efforts, constant progress in their jobs, make greater achievements. Every year I have progress, the growth of believe will get greater returns, I will my biggest contribution to the development of the company, believe inyourself do better next year!I wish you all work study progress in the year to come.。
电力词汇供电和用电波形质量Waveformquality电压和电流波形的正弦形程度。
城市供电Urbanpowersupply大面积停电Large-scaleconsumeroutage大型企业供电Powersupplyoflargeenterprise单边供电Singlesidefeeding单回路供电Single-circuitpowersupply单相供电Single-phasepowersupply地铁供电Powersupplytosubway地下供电Undergroundpowersupply电力牵引供电PowersupplyofelectrictractionEL力销售Electricitymarketing电力营销Electricitymarketing以满足人们的电力消费需求为目的的基本活动。
电能质量Electricpowerquality电压波动和变Voltagefluctuationandflicker一系列电压随机变动或工频电压包络线的周期性变化，以及由此引起的照明闪变。
it压和电流不平衡度Unsymmetryofvoltageandcurrent各相电压、电流幅值和相位的不对称程度。
电压质量Voltagequality动态电压恢复器Dynamicvoltagerecovery(DVR)能通过串联变压器向馈线注入可控幅值、相角和频率的电压，从而恢复负荷侧的电压质量。
独立电源Independentelectricsupply多回路供电Multiplefeed多相供电Polyphasepowersupply高层建筑物供电High-risebuildingpowersupply高压供电High-voltagepowersupply供电Powersupply供电点Power-supplypointDL/T一用户受电装置接入供电网中的位置。
供电电源Power-supplysource供电方案Schemeofpowersupply电力供应的具体实施计划。
北师大版教材高考英语第二轮复习书面表达专题之模块话题作文精选（必修一至选修八）假如你叫陈宇，你的英国笔友Mike在上次来信中谈到了低碳生活这个话题。
最近几个月校倡导学生过低碳生活、过节约生活、做有责任感的公民，引导学生从出行、购物、用水、家电和餐具使用方面反省自己的生活方式。
请你用英文给Mike回信。
回信要点如下：1．你对低碳生活的理解2．你校展开的活动3．你最近生活方式的改变（至少选择三个方面）注意：1．词数为100左右；2．参考词汇低碳生活low carbon lifestyle 3．信的开头和结尾已为你写好（不计入你所写词数）Dear Mike,How are things going? In your last letter you talked about low carbon life. Now I’d like to share my understanding of it and my experience in the past few months.With the environment problem coming into attention, it is extremely important that we take action to protect our planet. As more people are determined to make a difference, low carbon lifestyle provides us with the perfect opportunity to do it. Interestingly, our school called on students to develop a low carbon lifestyle and become a responsible citizen several months ago. In response to the appeal, I have made some changes in my way of life, which ranges from transportation to water saving. For example, instead of asking my parents to drive me to school, I take a bus to and from school. just like my schoolmates, I now refuse to use disposable chopsticks. At home, I even persuade my parents to reuse water, even though it is not so convenient. TV and computer are important entertainment for my family, but we sometimes read instead, which, I think, may help relieve the shortage of electricity.I’m really glad to communicate with you about this topic.书面表达：（必修一Unit 2）中国女药学家屠呦呦在2015年获得了诺贝尔医学奖，中国人的骄傲。
电磁波吸收材料的英语Electromagnetic wave absorbing materials, commonly referred to as microwave absorbers or radar absorbers, are substances that effectively convert incident electromagnetic energy into other forms of energy, such as heat, without reflecting or transmitting it. These materials play a crucial role in various applications ranging from military stealth technology to consumer electronics, where they are employed to reduce electromagnetic interference (EMI) and electromagnetic compatibility (EMC) issues.The need for electromagnetic wave absorbing materials arose in the mid-20th century, when radar systems were developed for military purposes. Since then, the field has evolved significantly, with the advent of newer technologies and materials that offer superior absorption properties. The basic principle behind electromagnetic wave absorption is the conversion of electromagnetic energy into other forms of energy, primarily heat, through interactions between the material's constituents and the incident waves.The properties of electromagnetic wave absorbing materials are primarily determined by their composition, structure, and morphology. These materials are typically composed of a matrix reinforced with absorptive particles, such as carbon black, ferromagnetic particles, or conductive polymers. The matrix acts as a support for the absorptive particles, while the particles themselves absorb the incident electromagnetic waves.The absorption mechanism of these materials involves several complex processes, including dielectric loss, magnetic loss, and thermal loss. Dielectric loss occurs when the incident waves interact with the electric field of the material, causing a redistribution of charge within the material. Magnetic loss, on the other hand, involves the interaction of the incident waves with the magnetic field of the material, resulting in the alignment and rearrangement of magnetic moments. Thermal loss occurs when the absorbed energy is converted into heat, causing a rise in temperature within the material.The performance of electromagnetic wave absorbing materials is evaluated based on several parameters,including absorption coefficient, reflection coefficient, and bandwidth. The absorption coefficient quantifies the amount of incident electromagnetic energy absorbed by the material, while the reflection coefficient measures the amount of energy reflected from the material's surface. The bandwidth, on the other hand, represents the range of frequencies over which the material exhibits goodabsorption properties.In recent years, there has been a growing interest in the development of lightweight, thin, and flexible electromagnetic wave absorbing materials. These materials offer several advantages over traditional bulkier and heavier absorbers, including improved mechanical properties, ease of integration into devices, and cost-effectivenesss. To achieve these desired properties, researchers have been exploring novel materials and nanostructures, such ascarbon-based materials, ferromagnetic alloys, and metamaterials.Carbon-based materials, such as carbon nanotubes and graphene, have attracted significant attention due to their excellent electrical conductivity and high surface area.These materials can effectively absorb electromagnetic waves over a wide frequency range and convert them into heat. Ferromagnetic alloys, on the other hand, exhibit strong magnetic properties that enable them to absorb electromagnetic waves efficiently, especially at higher frequencies. Metamaterials, which are artificially structured composites with unique electromagnetic properties, offer the potential for tailored absorption characteristics and enhanced performance.In conclusion, electromagnetic wave absorbing materials play a crucial role in addressing electromagnetic interference and compatibility issues in various applications. With the ongoing research and development of novel materials and nanostructures, we can expect significant improvements in the performance andapplications of these materials in the future.**电磁波吸收材料：技术综述**电磁波吸收材料，通常被称为微波吸收器或雷达吸收器，是一种能有效将入射的电磁能量转化为其他形式能量的物质，如热量，而不进行反射或传输。
大工17春《大学英语3》在线测试1一、单项选择题〔共20 道试题，共80 分。
〕1. How much did you _____ all these things?A. spendB. costC. giveD. pay for总分值：4 分2. Smoking is __________ here. Could you move to the smoking zone please?A. forbiddenB. stoppedC. preservedD. ceased总分值：4 分3. He had often dreamed of retiring in England and had planned to ________ down in the country.A. breakB. comeC. putD. settle总分值：4 分4. I don't know ________ to deal with such matter.A. whatB. howC. whichD. /总分值：4 分5. I'm sorry to have started the meeting, I thought().A. you did not comeB. you were not comingC. you were not comingD. you are not coming总分值：4 分6. Although he failed in his attempts, his mother's __________ drove him on to continue his efforts.A. motivationB. encouragementC. intentionD. compulsion总分值：4 分7. They got a ________ result, and they were wild with joy.A. magicB. magicianC. magneticD. magical总分值：4 分8. Mary doesn't look happy today. She would rather Bob and Linda () each other any more.A. don't seeB. didn't seeC. havn't seeeD. won't see总分值：4 分9. I advise that they ________ to the government for a home improvement fund, but I'm not sure whether they can obtain it.A. applicantB. applyC. employD. qualify总分值：4 分10. Professor Smith promised to look ________ my paper, that is, to read it carefully before the thesis defense.A. afterB. overC. onD. into总分值：4 分11. He's been sought after by many young girls. I am really surprised you have an unfavorable ______ of him.A. thoughtB. impressionC. conceptD. notion总分值：4 分12. The poor police had never ____ of winning.A. stand a chanceB. get a chanceC. have a chanceD. stood a chance总分值：4 分13. She won't forgive him ______ he makes an apology to her.A. althoughB. onceC. ifD. unless总分值：4 分14. The essays should be ____ to the journal by Jan. 15, which is the deadline.A. saved upB. turned outC. sent offD. taken over总分值：4 分15. This time next week I'll be on vacation. Probably I ______ on a beautiful beach.A. am lyingB. have lainC. will be lyingD. will have lain总分值：4 分16. Their efforts to improve the production have been very _________, and they have been praised by the company for their contribution.A. effectiveB. efficientC. effectD. affective总分值：4 分17. It’s bad _________ for you to smoke in the public places where smoking is not allowed.A. behaviorB. actionC. mannerD. movement总分值：4 分18. Coal was formed out of dead forests by a long and slow _______ of chemical change.A. pressB. procedureC. successD. process总分值：4 分19. To do a good job in public speaking, one must be aware of the _______ issues, both nationally and internationlly.A. brilliantB. extensiveC. currentD. modern总分值：4 分20. Take it easy. It is all a ______ to an end.A. partB. meansC. choiceD. process总分值：4 分二、判断题〔共10 道试题，共20 分。
专业英语四级（完形填空）-试卷234(总分：100.00，做题时间：90分钟)一、 CLOZE(总题数：5，分数：100.00)1.PART IV CLOZEDecide which of the words given in the box below would best complete the passage if inserted in the corresponding blanks. The words can be used ONCE ONLY.（分数：20.00）__________________________________________________________________________________________解析：A. factB. continuouslyC. ignoreD. whenE. muchF. showsG. preventedH. playsI. limitedJ. unconsciouslyK. dataL. unpredictableM. toolsN. attendO. because In recent decades, scientists have become increasingly aware of the part the observer 1 in the scientific process. In the first place, the observer can work only with his experiences, and these are 2 by his senses and the instruments he uses to extend his senses. Ultraviolet light, electromagnetic fields, and atomic particles, for example, became known to us only as we devised 3 with which we could observe their effects. Consequently, our picture of the real world is always incomplete. Secondly, the observer is highly selective in choosing his 4. Life is a narrative of ever new and often 5 events. At any given moment, an individual is bombarded with sense experiences and can, if he desires, expose himself to more. But he is really interested in or concerned with only a few of these. Other experiences are consciously or 6 screened out as irrelevant to the task at hand. For example, as we read a book, we are often surrounded by sounds and activities that we 7, but by turning our attention to them we become conscious of their presence. What a scientist discovers depends, to a great extent, on what he is looking for— on the questions he is asking. Thus, academic disciplines differ in their study of human beings in large part 8 they ask different questions. Human beings live, so to speak, in a house with only a few windows of tinted and curved glass, through which we see the outside world. The glass colors and distorts our observations, and its effects can be determined only with 9 difficulty. Scientists are increasingly aware of the 10 that they work with sense data, not with the world itself.（分数：20.00）填空项1:__________________ （正确答案：H）填空项1:__________________ （正确答案：I）填空项1:__________________ （正确答案：M）填空项1:__________________ （正确答案：K）填空项1:__________________ （正确答案：L）填空项1:__________________ （正确答案：J）填空项1:__________________ （正确答案：C）填空项1:__________________ （正确答案：O）填空项1:__________________ （正确答案：E）填空项1:__________________ （正确答案：A）解析：解析：空格前的定冠词the提示此处应填入名词。
Abstract:High voltage currents play an instrumental role in the efficient transmission and distribution of electrical power across diverse sectors and geographical scales. This comprehensive analysis delves into the multifaceted aspects of high voltage currents, examining their fundamental principles, applications, safety considerations, environmental implications, technological advancements, and quality standards. The discussion aims to provide a holistic understanding of this critical component of modern electricity infrastructure, contributing to informed decision-making and fostering innovation in the field.I. Introduction (250 words)High voltage currents, defined as electric currents with voltages exceeding 1,000 volts in alternating current (AC) systems or 1,500 volts in direct current (DC) systems, are at the core of power transmission and distribution networks worldwide. Their importance lies in their ability to minimize energy losses during long-distance transmission, thereby enhancing overall system efficiency. This introductory section will outline the historical context, evolution, and significance of high voltage currents, setting the stage for the subsequent in-depth exploration.II. Fundamentals of High Voltage Currents (400 words)A. Electrical Principles: This subsection will delve into the physics underlying high voltage currents, including Ohm's Law, Kirchhoff's Laws, and the skin effect. It will explain how these principles contribute to the reduced resistive losses in high voltage systems compared to low voltage ones.B. Types of High Voltage Systems: A detailed examination of AC and DC high voltage systems, their characteristics, advantages, and limitations will be presented. This will include discussions on single-phase, three-phase, and multi-terminal HVDC systems, as well as their respective applications.C. Power Conversion and Conditioning: The role of transformers, circuit breakers, and other power conditioning equipment in managing high voltage currents will be elucidated. This will highlight the importance of thesecomponents in ensuring stability, reliability, and safety within high voltage networks.III. Applications and Benefits of High Voltage Currents (460 words)A. Long-Distance Power Transmission: The pivotal role of high voltage currents in enabling efficient, large-scale power transfer over vast distances will be discussed. Key factors such as line capacity, power factor correction, and voltage regulation will be addressed.B. Interconnecting Power Grids: The facilitation of regional and international power exchanges through high voltage interconnections will be explored. This will encompass topics like grid synchronization, load balancing, and the integration of renewable energy sources.C. Industrial and Commercial Applications: The use of high voltage currents in various industrial processes, commercial facilities, and specialized applications, such as electric railways and large-scale data centers, will be examined. The discussion will emphasize the unique challenges and solutions associated with each application.IV. Safety Considerations and Regulations for High Voltage Currents (290 words)A. Electrical Hazards and Prevention: This section will detail the potential dangers posed by high voltage currents, including arc flashes, electrocution, and fires. It will outline best practices and mandatory safety measures, such as insulation, grounding, and personal protective equipment, to mitigate these risks.B. International and National Standards: An overview of key regulatory frameworks governing high voltage systems, such as IEEE, IEC, and NEC standards, will be provided. The roles of these standards in ensuring consistency, interoperability, and safety across the global power sector will be emphasized.V. Environmental Implications and Sustainability (270 words)A. Emissions and Energy Efficiency: The contribution of high voltage currents to reducing greenhouse gas emissions and improving overall energyefficiency in power systems will be assessed. This will include discussions on the life-cycle assessment of high voltage infrastructure and its impact on the carbon footprint of electricity generation and consumption.B. Electromagnetic Fields (EMFs) and Human Health: The scientific debate surrounding EMF exposure from high voltage systems and its potential health effects will be examined, along with measures taken to minimize public exposure within regulatory limits.VI. Technological Advancements and Future Trends (250 words)A. Smart Grid Technologies: The integration of advanced monitoring, control, and communication technologies into high voltage systems, enabling enhanced grid resilience, flexibility, and responsiveness, will be discussed. Particular emphasis will be placed on the role of synchrophasors, distributed energy resources, and artificial intelligence.B. Emerging Technologies: Cutting-edge developments in high voltage engineering, such as superconducting cables, hybrid AC/DC grids, and modular multilevel converters, will be explored. Their potential to revolutionize power transmission and distribution, addressing future challenges like increased renewable penetration and electrification of transportation, will be highlighted.VII. Conclusion (100 words)Summarizing the key findings and insights from the preceding sections, this conclusion will reiterate the vital role of high voltage currents in modern society and emphasize the ongoing need for research, innovation, and stringent quality standards to ensure their continued safe, efficient, and sustainable operation in the face of evolving energy landscapes.Total Word Count: 2,.jpg。
一，Vladimir A. Rakov (SM’96–F’03) received theMaster’s and Ph.D. degrees from Tomsk Poly-technical University (Tomsk Polytechnic), Tomsk,Russia in 1977 and 1983, respectively.From 1977 to 1979, he was an Assistant Professorof Electrical Engineering at Tomsk Polytechnic. In1978, he became involved in lightning research at theHigh Voltage Engineering, a division of Tomsk Poly-technic, where from 1984 to 1994, he held the posi-tion of Director of the Lightning Research Labora-tory.In 1985, he received the rank of Senior Scientistthe High Voltage Research Institute. In 1991, he joined the faculty of the Depart- ment of Electrical and Computer Engineering at the University of Florida (UF), Gainesville, where he is a Professor in the Department of Electrical and Com- puter Engineering. He is the author or coauthor of over 30 patents, the book Lightning: Physics and Effects (Cambridge, U.K.: Cambridge Univer. Press, 2003), and about 300 papers and technical reports on various aspects of light- ning, with over 100 papers published in reviewed journals.Dr. Rakov has been named an Inventor of the USSR (1986) and receiveda Silver Medal from the (USSR) National Exhibition of Technological Achievements (1987). He is a Fellow of the American MeteorologicalSociety, Chairman of the Technical Committee on Lightning of the biennial International Zurich Symposium on Electromagnetic Compatibility, and former chairman of the AGU Committee on Atmospheric and Space ElectricityVladimir A. Rakov (SM’96–F’03)于1977年和1983年在俄罗斯，托木斯克州，托木斯克科技大学（托木斯克理工学院）分别获得了硕士和博士学位。
English translationThe E- Behind EverythingElectricity and magnetism run nearly everything we plug in or turn on. Although it’s something we take for granted, it has taken hundreds of years of experimentation and research to reach the point where we flick a switch and the lights go on.People knew about electricity for a long time. Ancient Greeks noticed that if they rubbed a piece of amber, feathers would stick to it. You’ve experienced a similar thing if you’ve ever had your hair stick up straight after you combed it, or had your socks stick together when you removed them from the drier. This is called static electricity, but back then nobody knew how to explain it or what to do with it.Experiments using friction to generate static electricity led to machines that could produce large amounts of static electricity on demand. In 1660 German Otto von made the first electrostatic generator with a ball of sulfur and some cloth. The ball symbolized the earth, and he believed that this little replica of the e arth would shed part of its electric “soul” when rubbed. It worked, and now scientists could study electric shocks and sparks whenever they wanted.As scientists continued to study electricity, they began thinking of it as an invisible fluid and tried to capture and store it. One of the first to do this was Pieter van, Holland. In 1746 he wrapped a water-filled jar with metal foil and discovered that this simple device could store the energy produced by an electrostatic generator. This device became known as the jar. were very important in other people’s experiments, such as Benjamin Franklin’s famous kite experiment. Many people suspected that lightning and static electricity were the same thing, since both crackled and produced bright sparks. In 1752 Franklin attached a key to a kite and flew it in a storm-threatened sky. (NOTE that Franklin did not fly a kite in an actual storm. NEVER do that!) When a thundercloud moved by, the key sparked. This spark charged the jars and proved that lightning was really electricity. Like many experimenters and scientists Franklin used one discovery to make another. Franklin was not the only scientist inspired to conduct experiments with electricity. In the 1780s, the Italian scientist Luigi m ade a dead frog’s leg move by means of an electric current. called this “animal electricity.” He thought that the wet animal tissue generated electricity when it came in contact with metal probes. He even suggested that the soul was actually Italian Alessandro Volta was skeptical of con clusions. In 1799 he discovered that it wasn’t animal tissue alone producing the electric current at all. Volta believed that the current was actually caused by the interaction of water and chemicals in the animal tissue with the metal probes. Volta stacked metal disks separated by layers of cardboard soaked in salt water. This so-called voltaic pile produced an electric current without needing to be charged like a jar. This invention is still around today, but we call it the battery.Volta’s pile was a lot different from the batteries you put in your Discman. It was big, ugly, and messy, but it worked, making Volta the first person to generate electricity with a chemical reaction. His work was so important that the term volt—the unit of electrical tension or pr—is named in his honor. As for Galvani, although he was proven wrong, his work stimulated research on electricity and the body. That research eventually proved that nerves do carry electrical impulses, an important medical discovery. Like electricity, magnetism was baffling to the earliest researchers. Today manufactured magnets are common, but in earlier timesthe only available magnets were rare and mysterious rocks with an unexplainable attraction for bits of iron. Explanations of the way they work sound strange today. For example, in the 1600, English doctor William Gilbert published a book on magnetism. He thought that these strange substances, called “lodestones,” had a soul that accounted for the attraction of a lodestone to iron and steel. The only real use for lodestones was to make compasses, and many thought the compass needle’s movement was in response to its attraction to the earth’s “soul.” By 1800, after many years of study, scientists began wondering if these two mysterious forces—electricity and magnetism—were related. In 1820 Danish physicist Hans Oersted showed that whenever an electric current flows through a wire, it produces a magnetic field around the wire. French mathematician André-Marie used algebra to come up with a mathematical formula to describe this relationship between electricity and magnetism. He was one of the first to develop measuring techniques for electricity. The unit for current, the ampere, abbreviated as amp or as A, is named in his honor. Groundbreaking experiments in electromagnetism were conducted by British scientist Michael Faraday. He showed that when you move a loop of a wire in a magnetic field, a little bit of current flows through the loop for just a moment. This is called induction. Faraday constructed a different version of it called the induction ring. In later years, engineers would use the principle of the induction ring to build electrical transformers, which are used today in thousands of electrical and electronic devices. Faraday also invented a machine that kept a loop of wire rotating near a magnet continuously. By touching two wires to the rotating loop, he could detect the small flow electric current. This machine used induction to produce a flow of current as long as it was in motion, and so it was an electromagnetic generator. However, the amount of electricity it produced was very tiny. There was still another use for induction. Faraday also created a tiny electric motor—too small to do the work of a steam engine but still quite promising. For thousands of years electricity and magnetism were subjects of interest only to experimenters and scientists. Nobody thought of a practical way of using electricity before the 1800s and it was of little interest to most people. But by Faraday’s time invento rs and engineers were gearing up to transform scientific concepts into practical machines.Telegraphs and TelephonesOne of the most important ways that electricity and magnetism have been put to use is making communication faster and easier. In this day o f instant messaging, cell phones, and pagers, it’s hard to imagine a time when messages had to be written and might spend weeks or even months reaching their destination. They had to be carried great distances by ships, wagon, or even by horseback—you coul dn’t just call somebody up to say hello. That all changed when inventors began using electricity and magnetism to find better ways for people to talk to each other. The telegraph was first conceived of in the 1700s, but few people pursued it. By the 1830s, however, advancements in the field of electromagnetism, such as those made by Alessandro Volta and Joseph Henry, created new interest in electromagnetic communication. In 1837, English scientist Charles Wheatstone opened the first com telegraph line between London and Camden Town, a distance of 1.5 miles. Building on, Samuel Morse, an American artist and inventor, designed a line to connect Washington, DC and Baltimore, Maryland in 1844. Morse’s telegraph was a simple device that used a battery, a switch, and a small electromagnet, but it allowed people miles apart to communicate instantly. Although Morse is often credited with inventing the telegraph, his greatest contribution was actually Morse, a special language designed for the telegraph. Morse'scommercialization of the telegraph spread the technology quickly. In 1861 California was connected to the rest of the United States with the first transcontinental telegraph line. Five years later, engineers found a way of spanning the Atlantic Ocean with telegraph lines, thus connecting the United States and Europe. This was an enormous and challenging job. To do it engineers had to use a huge ship called The Great Eastern to lay the cable across the ocean. It was the only ship with enough room to store all that cable. The world was connected by wire before the nation was connected by rail—the transcontinental railroad wasn’t completed until 1869! The telegraph was the key to fast, efficient railroad service. The railroads and the telegraph expanded side-by-side, crisscrossing every continent, except Anta, in the late 1800s. In the late 19th and early 20th centuries, telegraphy became a very lucrative business for companies such as Western Union. It also provided women with new career options. As convenient as the telegraph was, people dreamt of hearing the voices of loved ones who lived far away. Pretty soon, another instrument to communicate across distances was invented. Alexander Graham Bell, a teacher and inventor, worked with the deaf and became fascinated with studying sound. In 1875, Bell discovered a way to convert sound waves to an undulating current that could be carried along wires. This helped him invent the telephone. The first phone conversation was an inadvertent one between Bell and Watson, his ass istant in the next room. After spilling some acid, Bell said “Mr. Watson, come here.I want you.” He patented his device the same year. Early phone service wasn’t as portable and convenient as today’s. At first, telephones we connected in pairs. You could call only one person, and they could only call you. The telephone exchange changed all that. The first exchange was in New Haven, Connecticut in 1878. It allowed people who subscribed to it to call one another. Operators had to connect the calls, but in 1891 an automatic exchange was invented. Some problems had to be solved, though, before long-distance telephoning could work. The main one was that the signal weakened with distance, disappearing if the telephone lines were too long. A solution was found in 1912 with a way to amplify electrical signals, and transcontinental phone calls were possible. A test took place in 1914, and the next year, Bell, who was in New York, called Watson, who was in San Francisco. He said the same thing he had said during the first phone conversation. Watson’s answer? “It will take me five days to get there now!”Plc development1.1 MotivationProgrammable Logic Controllers (PLC), a computing device invented by Richard E. Morley in 1968, have been widely used in industry including manufacturing systems, transportation systems, chemical process facilities, and many others. At that time, the PLC replaced the hardwired logic with soft-wired logic or so-called relay ladder logic (RLL), a programming language visually resembling the hardwired logic, and reduced thereby the configuration time from 6 months down to 6 days [Moody and Morley, 1999].Although PC based control has started to come into place, PLC based control will remain the technique to which the majority of industrial applications will adhere due to its higher performance, lower price, and superior reliability in harsh environments. Moreover, according to a study on the PLC market of Frost and Sullivan [1995], an increase of the annual sales volume to 15 million PLCs per year with the hardware value of more than 8 billion US dollars has been predicted, though the prices of computing hardware is steadily dropping. The inventor of the PLC, Richard E Morley, fairly considers the PLC market as a 5-billion industry at the present time.Though PLCs are widely used in industrial practice, the programming of PLC based control systems is still very much relying on trial-and-error. Alike software engineering, PLC software design is facing the software dilemma or crisis in a similar way. Morley himself emphasized this aspect most forcefully by indicating [Moody and Morley, 1999, p. 110]:`If houses were built like software projects, a single woodpecker could destroy civilization.” Particularly, practical problems in PLC programming are to eliminate software bugs and to reduce the maintenance costs of old ladder logic programs. Though the hardware costs of PLCs are dropping continuously, reducing the scan time of the ladder logic is still an issue in industry so that low-cost PLCs can be used.In general, the productivity in generating PLC is far behind compared to other domains, for instance, VLSI design, where efficient computer aided design tools are in practice. Existent software engineering methodologies are not necessarily applicable to the PLC based software design because PLC-programming requires a simultaneous consideration of hardware and software. The software design becomes, thereby, more and more the major cost driver. In many industrial design projects, more than SO0/a of the manpower allocated for the control system design and installation is scheduled for testing and debugging PLC programs [Rockwell, 1999].In addition, current PLC based control systems are not properly designed to support the growing demand for flexibility and reconfigurability of manufacturing systems. A further problem, impelling the need for a systematic design methodology, is the increasing software complexity in large-scale projects.1.2 Objective and Significance of the ThesisThe objective of this thesis is to develop a systematic software design methodology for PLC operated automation systems. The design methodology involves high-level description based on state transition models that treat automation control systems as discrete event systems, a stepwise design process, and set of design rules providing guidance and measurements to achieve a successful design. The tangible outcome of this research is to find a way to reduce the uncertainty in managing the control software development process, that is, reducing programming and debugging time and their variation, increasing flexibility of the automation systems, and enabling software reusability through modularity. The goal is to overcome shortcomings of current programming strategies that are based on the experience of the individual software developer.A systematic approach to designing PLC software can overcome deficiencies in the traditional way of programming manufacturing control systems, and can have wide ramifications in several industrial applications. Automation control systems are modeled by formal languages or, equivalently, by state machines. Formal representations provide a high-level description of the behavior of the system to be controlled. State machines can be analytically evaluated as to whether or not they meet the desired goals. Secondly, a state machine description provides a structured representation to convey the logical requirements and constraints such as detailed safety rules. Thirdly, well-defined control systems design outcomes are conducive to automatic code generation- An ability to produce control software executable on commercial distinct logic controllers can reduce programming lead-time and labor cost. In particular, the thesis is relevant with respect to the following aspects.Customer-Driven ManufacturingIn modern manufacturing, systems are characterized by product and process innovation, become customer-driven and thus have to respond quickly to changing system requirements. A majorchallenge is therefore to provide enabling technologies that can economically reconfigure automation control systems in response to changing needs and new opportunities. Design and operational knowledge can be reused in real-time, therefore, giving a significant competitive edge in industrial practice.Higher Degree of Design Automation and Software QualityStudies have shown that programming methodologies in automation systems have not been able to match rapid increase in use of computing resources. For instance, the programming of PLCs still relies on a conventional programming style with ladder logic diagrams. As a result, the delays and resources in programming are a major stumbling stone for the progress of manufacturing industry. Testing and debugging may consume over 50% of the manpower allocated for the PLC program design. Standards [IEC 60848, 1999; IEC-61131-3, 1993; IEC 61499, 1998; ISO 15745-1, 1999] have been formed to fix and disseminate state-of-the-art design methods, but they normally cannot participate in advancing the knowledge of efficient program and system design.A systematic approach will increase the level of design automation through reusing existing software components, and will provide methods to make large-scale system design manageable. Likewise, it will improve software quality and reliability and will be relevant to systems high security standards, especially those having hazardous impact on the environment such as airport control, and public railroads.System ComplexityThe software industry is regarded as a performance destructor and complexity generator. Steadily shrinking hardware prices spoils the need for software performance in terms of code optimization and efficiency. The result is that massive and less efficient software code on one hand outpaces the gains in hardware performance on the other hand. Secondly, software proliferates into complexity of unmanageable dimensions; software redesign and maintenance-essential in modern automation systems-becomes nearly impossible. Particularly, PLC programs have evolved from a couple lines of code 25 years ago to thousands of lines of code with a similar number of 1/O points. Increased safety, for instance new policies on fire protection, and the flexibility of modern automation systems add complexity to the program design process. Consequently, the life-cycle cost of software is a permanently growing fraction of the total cost. 80-90% of these costs are going into software maintenance, debugging, adaptation and expansion to meet changing needs [Simmons et al., 1998].Design Theory DevelopmentToday, the primary focus of most design research is based on mechanical or electrical products. One of the by-products of this proposed research is to enhance our fundamental understanding of design theory and methodology by extending it to the field of engineering systems design. A system design theory for large-scale and complex system is not yet fully developed. Particularly, the question of how to simplify a complicated or complex design task has not been tackled in a scientific way. Furthermore, building a bridge between design theory and the latest epistemological outcomes of formal representations in computer sciences and operations research, such as discrete event system modeling, can advance future development in engineering design. Application in Logical Hardware DesignFrom a logical perspective, PLC software design is similar to the hardware design of integrated circuits. Modern VLSI designs are extremely complex with several million parts and a product development time of 3 years [Whitney, 1996]. The design process is normally separated into acomponent design and a system design stage. At component design stage, single functions are designed and verified. At system design stage, components are aggregated and the whole system behavior and functionality is tested through simulation. In general, a complete verification is impossible. Hence, a systematic approach as exemplified for the PLC program design may impact the logical hardware design.1.3 Structure of the ThesisFigure 1.1 illustrates the outline of the following thesis. Chapter 2 clarifies the major challenges and research issues, and discourses the relevant background and terminology. It will be argued that a systematic design of PLC software can contribute to higher flexibility and reconfigurability of manufacturing systems. The important issue of how to deal with complexity in engineering design with respect to designing and operating a system will be debated. The research approach applied in this thesis is introduced starting from a discussion of design theory and methodology and what can be learnt from that field.Chapter 3 covers the state-of-the-art of control technology and the current practice in designing and programming PLC software. The influences of electrical and software engineering are revealed as well as the potentially applicable methods from computer science are discussed. Pros and cons are evaluated and will lead to the conclusion that a new methodology is required that suffices the increasing complexity of PLC software design.Chapter 4 represents the main body of the thesis and captures the essential features of the design methodology. Though design theory is regarded as being in a pre- scientific stage it has advanced in mechanical, software and system engineering with respect to a number of proposed design models and their evaluation throughout real-world examples. Based on a literature review in Chapter 2 and 3 potential applicable design concepts and approaches are selected and applied to context of PLC software design. Axiomatic design is chosen as underlying design concept since it provides guidance for the designer without restriction to a particular design context. To advance the design concept to PLC software design, a formal notation based on statechart formalism is introduced. Furthermore, a design process is developed that arranges the activities needed in a sequential order and shows the related design outcomes.In Chapter 5, a number of case studies are given to demonstrate the applicability of the developed design methodology. The examples are derived from a complex reference system, a flexible assembly system. The achieved insights are evaluated in a concluding paragraph.Chapter 6 presents the developed computerized design tool for PLC software design on a conceptual level. The software is written in Visual Basic by using ActiveX controls to provide modularity and reuse in a web-based collaborative programming environment. Main components of the PLC software are modeling editors for the structural (modular) and the behavioral design, a layout specification interface and a simulation engine that can validate the developed model. Chapter 7 is concluding this thesis. It addresses the achievements with respect to the research objectives and questions. A critical evaluation is given alongside with an outlook for future research issues.电力的故事当我们插上电源,打开旋钮,电和磁差不多在每样东西上都运行着,今天我们知道这是什么,这一些花了人们上百年时间的实验和研究来达到这一点—当我们按下按钮时,光亮已经开始，人们对电的了解已经有很长一段时间了.古希腊人注意到,摩擦一块琥珀,羽毛将能被吸住.你已经经历过相类似的事情,当你梳头时,头发将垂直竖起,当你从干燥机中拿袜子时,袜子也会粘在一起.这被称作静电.但是在以前人们不知道如何解释此类现象或如何应用这种现象，使用摩擦产生的静电来带动机器的实验可以产生大量所需要的静电.在1660年,德国人Otto von Guericke用一个硫磺球和一些布制造了第一台静电发电机.硫磺球象征大地,他深信这种小型地球复制品被摩擦时将流出电的灵魂,他成功了,现在的科学家可以在任何想要的时候来研究电击和电火花.随着科学家们持续对电的研究,他们开始认为它以一种看不见的方式流动,并试图去捕获并储存.第一次去做这项研究的是荷兰Leyden的Pieter van Musschenbroek.1746,他用一个金属箔片包一个装满水的罐子,发现这种简单的设备能储存由静电发电机产生的能量.这个设备后来著名的莱顿瓶.莱顿瓶在其他人的实验中有非常重要的作用.如Benjamin Franklin著名的风筝实验.许多人认为闪电和静电是同一种东西,由于双方碰撞产生明亮的电火花.1752年, Franklin将一把钥匙绑在风筝上,在一个暴风即将来临的天气里放飞(请记住Franklin不是在一个真正的暴风寸中放飞的,永远不要这样做),当一块雷雨云经过时,钥匙被闪电击中,闪电充满莱顿瓶,由此证明闪电实际也是一种电力.同其他实验人和科学家一样, Franklin用一个发现来做另外一个. Franklin并不是唯一的在电力实验方面灵光突现的科学家.18世纪80年代,意大利的科学家Luigi Galvani用电流让一只切断的青蛙的腿移动. Galvani称之为生物电.他认为当潮湿的动物组织同金属探测针接触时产生电能.他甚至大胆预测精神也是一种电能。
a r X i v :0804.4232v 1 [h e p -p h ] 26 A p r 2008JLAB-THY-08-815Electromagnetic and strong contributions to dAu soft coherentinelastic diffraction at RHICV.Guzey 1,∗and M.Strikman 2,†1Theory Center,Jefferson Lab,Newport News,VA 23606,USA2Department of Physics,Pennsylvania State University,University Park,PA 16802,USAAbstractWe estimate electromagnetic (ultra-peripheral)and strong contributions to dAu soft coherent inelastic diffraction at RHIC,dAu →XAu .We show that the electromagnetic contribution isthe dominant one and that the corresponding cross section is sizable,σdAu →XAu e .m .=214mb,which constitutes 10%of the total dAu inelastic cross section.PACS numbers:24.20.Ht,25.45.De,25.75.-qDeuteron–Gold(dAu)collisions constitute an essential part of the present physics pro-gram of the Relativistic Heavy Ion Collider(RHIC).Ultra-peripheral collisions(UPC)of ions of deuterium and Gold(or any other ions)are processes,where the colliding nuclei are separated by the transverse distance(impact parameter)larger than the sum of the deuteron and Gold radii.In this case,the heavier ion of Au acts as a source of quasi-real photons of a very high energy(the photonflux produced by deuterium is negligibly small compared to that by Au)and,hence,one effectively studies the interaction of photons with deuterons, dAu→dγAu→XAu[1,2].At RHIC,dAu ultra-peripheral collisions were studied in the following channels:dAu→dAuρ0and dAu→npAuρ0[3],and dAu→npAu[4].The cross section of the latter reaction was normalized to the theoretical prediction,σdAu→npAu=1.38b[5].This value is large and should be compared to the measured total dAu inelastic cross section,σdAu→X=2.26b[1]. SinceσdAu→npAu is so large,the dAu→npAu yield was used to determine the absolute normalization of the RHIC dAu data.In this paper,we consider yet another channel of dAu UPC,namely,deuteron inelastic diffraction,dAu→dγAu→XAu,where X denotes products of the deuteron inelastic=214mb, dissociation.Wefind that the corresponding cross section is sizable,σdAu→XAue.m.which constitutes10%of the total dAu inelastic cross section.Although the discussed cross section is only∼10%of the total inelastic cross section,it may contribute a larger fraction of the signal in certain cases.For example,if one considers the leading pion or nucleon production at small transverse momenta p t,one observes that the multiplicity of such processes is about the same in pN andγN interactions.At the same time,the A-dependence of the forward hadron multiplicity for x F>0.4(x F is the fraction of the projectile’s momentum carried by the leading hadron)is≈A−1/3.Hence theγN and pN interactions can give comparable contributions in the considered case.We also estimate the strong contribution to dAu→XAu soft coherent inelastic diffraction andfind that the corresponding cross section is rather small,σdAu→XAu=22mb.ddThe cross section of deuteron inelastic diffraction in dAu ultra-peripheral scattering reads, see e.g.[1,2],(s)=2 ωmaxωmin dωdNγ(ω)σdAu→XAue.m.photon-nucleon cross section;s is the total invariant energy squared per nucleon(√dω=Z2αωγ +1γ=2Z2α2 K20(x)−K21(x),(2)where Z is the electric charge(Z=79for Au);α≈1/137is thefine-structure constant;γis the Lorentz factor of the fast moving Au;b is the distance between the centers of Au and the deuteron in the transverse plane(impact parameter),which should be larger than the sum of the corresponding Au and deuteron radii,R A and R d;K0and K1are modified Bessel functions;x=(R A+R d)ω/γ.Note also that we omitted the negligibly small contribution of the K20/γ2term,when going from thefirst to the second line of Eq.(2).The maximal energy of the exchanged photon,ωmax,is determined by the Lorentz-contracted nuclear size,ωmax=γ/R A.The minimal photon energy,ωmin,is termined by the threshold of the inelasticγ+p→∆(1232)reaction.In the proton rest frame,ωmin=0.3 GeV.For the evaluation ofσdAu→XAue.m.using Eq.(1),we used the following input.At the current RHIC energy of√10-310-210-1100101102101011022σ d N /d ω [m b /G e V ]ω [GeV]FIG.1:The integrand of Eq.(1),2σγptot (ω)dN γ(ω)/dω,as a function of the photon energy ωin thedeuteron rest frame.A direct evaluation of Eq.(1)using the input described above givesσdAu →XAue .m .=214mb .(3)This value is quite sizable:it constitutes 10%of the total dAu inelastic cross section,σdAu →X =2.26b [1].The application of Eq.(1)to inelastic diffraction in deuteron-Lead UPC at the LHCenergy (√deuteron dissociation,dAu→ing the completeness of these two diffractive states,the sum of the corresponding cross sections can be expressed asX=d,pnσdAu→XAu= d2b d2r t|ψD(r t)|2× 1−exp −σpN tot2 −σnN tot2 +σNN el e−r2t/(4B el)T(b) 2.(4) In this equation,b is the transverse distance between the centers of Au and d;r t is the transverse distance between the proton and neutron in the deuteron;ψD(r t)is the deuteron wave function;σpN tot andσnN tot are respectively the proton-nucleon and neutron-nucleon total scattering cross sections(for the purpose of the following discussion,it is convenient todistinguish between the two cross sections);σNNelis the elastic nucleon-nucleon(NN)cross section;B el is the slope of the NN elastic amplitude;T(b)is the so-called optical density of the nucleus of Au,T(b)= dzρA(r),whereρA(r)is the nuclear density[17].The real part of the NN scattering amplitude is neglected in Eq.(4).In the following analysis,we neglect the contribution of the last term in the exponent inEq.(4),which is suppressed by the smallness of the elastic cross section,σNNel /σNNtot≈1/5at√2T b+r t2T b−r t2T b+r t2T b−r tdispersion.This allows one to expand the exponents in Eq.(5)aroundσNNtot[11]and to obtainσdAu→XAu dd =(σNNtot)2ωσ2 2×exp −σNN tot T b+r t2 ,(6)whereωσis a parameter describing the dispersion of P(σ)around its maximum and isproportional toσNN→XNdd ,the cross section of inelastic diffraction in NN scattering.At√np nFIG.2:The schematic representation of dAu →XAu coherent inelastic diffraction as a sum of two contributions,when either the neutron (left picture)or the proton (right picture)diffracts inelastically.We found that the corresponding cross section is sizable,σdAu →XAue .m .=214mb,which con-stitutes 10%of the total dAu inelastic cross section.The same reaction can also proceed through the strong interactions.We derived an approximate expression for the cross sec-tion of dAu →XAu soft coherent inelastic diffraction and estimated it to be rather small,σdAu →XAu dd =22mb.We also estimated the cross section of deuteron-Lead inelastic diffraction in ultra-peripheral dP b →dγP b →XP b scattering at the LHC energies (√[3]S.Timoshenko[STAR 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